Wells are generally drilled into the ground or ocean bed to recover natural deposits of oil and gas, as well as other desirable materials that are trapped in geological formations in the Earth's crust. Wells are typically drilled using a drill bit attached to the lower end of a “drill string.” Drilling fluid, or mud, is typically pumped down through the drill string to the drill bit. The drilling fluid lubricates and cools the bit, and may additionally carry drill cuttings from the wellbore back to the surface.
In various oil and gas exploration operations, it may be beneficial to have information about the subterranean formations that are penetrated by a wellbore. For example, certain formation evaluation schemes may include measurement and analysis of the formation pressure and permeability. These measurements may be essential to predicting the production capacity and production lifetime of the subterranean formation. In some implementations, pump systems may be used to draw and pump formation fluid from subterranean formations. In some implementations, pump systems may be used to pump injection fluid from a downhole tool into the subterranean formations. A downhole string (e.g., a drill string, coiled tubing, slickline, wireline, etc.) may include one or more pump systems depending on the operations to be performed using the downhole string.
Log-inject-log programs may be used to test the formation. A formation tester may include a sample chamber loaded with injection fluid. A first measurement may be made of the subterranean formation, and then the injection fluid may be injected into the subterranean formation. For example, the injection fluid may be injected into the subterranean formation so as to replace the in-situ fluids. After the injection, a second measurement of the subterranean formation may be made. Flow control may be desired when injecting fluids into the subterranean formation between measurements. However, traditional pump systems may be limited in operation by the range of flow rates that may be achieved during injection, or may be limited by the ability to control the flow rates that may be achieved during injection.